The invention relates to a protective cap for a sensor including a sensor element, which is disposed in a housing and includes a connection side and a measuring side, for determining gases in gas mixtures. The protective cap delimits a sensor element chamber and an antechamber in order to protect the sensor element on the measuring side. Furthermore, the invention relates to a gas sensor equipped with a protective cap.
Gas sensors are used for determining gases in gas mixtures by being disposed, for example, in a gas stream so that a part of the gas stream flows past the sensor element. In doing so, protective caps described at the start are used in order to protect sensor elements from undesirable components of the gas mixture and/or to ensure an optimized incident flow at the sensor element.
Gas sensors having a protective cap are the subject matter of DE 10 2004 050 222 A1 and DE 10 2005 012 449 A1 by way of example. However, it has been found that the known protective caps do not protect the sensor element to a sufficient extent and do not ensure a defined incident flow at the sensor element. For example, in a NOx sensor used in a motor vehicle for analyzing the internal combustion-engine exhaust gases, the sensor element can be exposed to condensate particularly during cold start and the warm-up phase, which results in the sensor element being damaged by the deposition of pollutants. A damaged sensor element of this type supplies incorrect or even no signals so that the operation of the internal combustion engine is very adversely affected.
It is therefore the object of the invention to provide a protective cap and a gas sensor in which an entry of undesirable components of the gas mixture is effectively avoided and a defined incident flow at the sensor element is ensured at the same time.
The object is achieved according to the invention with a protective cap for a sensor comprising a sensor element, which is disposed in a housing and has a connection side and a measuring side, for determining gases in gas mixtures. The protective cap delimits a sensor element chamber and an antechamber in order to protect the sensor element on the measuring side. A condensate separator is arranged in the antechamber. Likewise, the object of the invention is achieved with a protective cap for a sensor comprising a sensor element, which is disposed in a housing and has a connection side and a measuring side, for determining gases in gas mixtures. The protective cap delimits a sensor element chamber and an antechamber that is in fluid connection with the sensor element chamber in order to protect the sensor element on the measuring side. A device for deviating the flow is provided between the sensor element chamber and the antechamber. Furthermore, a protective cap achieves the object of the invention by providing a device for accelerating the flow on the flow outlet side of the sensor element chamber.
Particularly preferable embodiments of the invention and a gas sensor having the protective cap of the invention are further described herein.
It is particularly preferred to arrange the at least one flow inlet of the antechamber at the measuring-side end of the antechamber. This measure prevents a dead space in which particles or fluid components could be deposited.
The condensate separator is preferably formed as an annular circumferential rim, which is open axially in the direction of the at least one flow inlet of the antechamber and is disposed on the radially inner wall of the antechamber. By virtue of this arrangement, the gas stream flowing into the antechamber is deviated, particles and/or fluid components of the gas stream being separated from the same. It is very advantageous to arrange the fluid connection between the sensor element chamber and the antechamber axially on the sensor-connection side of the condensate separator. This arrangement necessitates a recirculation area of the flow and thus contributes to the particularly effective separation of particles and/or fluid components of the gas stream.
The device for deviating the flow expediently includes at least one opening with a flow-guiding device. This measure effectively prevents a direct incident flow at the sensor element and thus avoids an uneven cooling of the sensor element.
It has proved to be particularly advantageous to form the device for accelerating the flow as a conical nozzle. The gas stream flowing past the sensor element can be adjusted particularly easily with regard to flow volume and flow velocity by way of a corresponding, constructive design of the conical nozzle.
According to a particularly preferred embodiment of the invention, the ante-chamber includes at least one flow outlet in addition to the at least one flow inlet, it being possible to branch off a partial stream from an incoming gas stream from the antechamber into the sensor element chamber with the aid of the fluid connection between the antechamber and the sensor element chamber. In this way, a defined partial stream can be branched off from the gas stream and routed past the sensor element.
According to a further preferred exemplary embodiment, a baffle plate is disposed upstream of the device for accelerating the flow so that the sensor element is not located directly in front of a flow outlet and, furthermore, the flow experiences a restriction.
According to a further, preferred exemplary embodiment, an additional cap having at least one flow outlet is disposed downstream of the device for accelerating the flow. The additional cap notably prevents the entry of undesirable particles and/or fluid components of the gas stream toward the sensor element through the flow outlet.
A gas sensor including a protective cap of the invention provides special advantages.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.